Just to be clear this is not a foliage bug but a object surface bug. You cannot snap object to the surface of the imported object either, the same way the paint tool will also not be able to “see” the object surface.
Several editor tools use visibility collision to determine where mesh surfaces are including snap to surface and foliage painting.
I believe there has been a change in behavior for the case where the Auto Generate Collision checkbox is not set. In version 4.12 the imported static mesh still has a collision model based on the triangles even if you don’t set the checkbox.
This can be seen in the Static Mesh viewer with the Collision button pressed. In 4.12 you can see the collision triangles but in 4.13 there is absolutely no collision. You can also see this in the editor viewport with the Visibility Collision view mode. In 4.13 the reimported mesh doesn’t show up, but in 4.12 it does.
Hey Jack, not related to this exact bug but to foliage, do you know something about this HISMC bug that’s currently in master it seems? 
Hey John,
Please create a new thread if you are experiencing a separate issue so we can investigate it as such.
Thanks!